1. Field of the Invention
The current invention relates generally to marking semiconductor dice having integrated circuits (ICs) and, more specifically, to a system for uniquely marking exterior surfaces of semiconductor dice in lots.
2. State of the Art
In conventional semiconductor device fabrication processes, a number of distinct semiconductor devices, such as memory chips or microprocessors, are fabricated on a semiconductor substrate, such as a silicon wafer. Each semiconductor wafer has a plurality of integrated circuit semiconductor dice (IC) arranged in rows and columns with the periphery of each IC being substantially rectangular or square. After the desired structures, circuitry, and other features of each of the semiconductor devices have been fabricated upon the semiconductor substrate, the substrate is typically singulated to separate the individual semiconductor devices from one another.
While semiconductor dice may carry information on the active surface thereof regarding the manufacturer, specifications, etc., such information cannot be easily read without the use of optical devices. Therefore, subsequent to the wafer dicing process, individual semiconductor dice are commonly subjected to a marking process wherein various easily read information is placed on the backside or inactive side of the semiconductor die for purposes of corporate identity, product differentiation and counterfeit protection.
Currently, the preferred method of marking packaged semiconductor dice is using a laser beam. Lasers are used to mark semiconductor dice with a manufacturer's logo, as well as alphanumeric marks and bar codes specifying the company's name, a part or serial number, or other information such as lot or die location. In particular, lasers have become especially useful in marking high volume production items such as bare or packaged semiconductor dice. The high speed and precision of laser marking makes their use highly desirable for high throughput automated processes. Unlike the previously utilized technique of ink stamping, laser marking is very fast, requires no curing time, produces a consistently high quality mark, and can take place at any point in the manufacturing process.
Traditionally, semiconductor devices are marked as a group of 25 to as many as 50 devices having similar parameters. Singulated semiconductor devices are characterized for compliance with certain criteria in order to determine their suitability, or lack thereof, for different potential uses. For example, devices may be separated based on operating speed wherein devices performing above a particular speed are placed in one group while devices functioning at a slower speed are placed into a different group. Carriers such as tubular magazines or bins 200 can be used to physically separate groups of devices 250 (FIG. 3). However, these carriers are unsuitable for recently developed semiconductor packages that are much-reduced in size, thickness and dimensions of individual features, such as leads for external connection to higher-level packaging.
One example of such state-of-the-art semiconductor device packages is a thin plastic package configuration identified as a Thin Small Outline Package, or TSOP. Another example is a Thin Quad Flat Pack, or TQFP. By way of comparison, such packages are dimensioned with a total package thickness, excluding lead fingers, of less than about one-half the thickness of a conventional plastic Small Outline J-lead package, or SOJ. These newer semiconductor device packages, with their smaller dimensions and more fragile components, are much more susceptible to inadvertent damage in handling than prior package designs and, at best, are only marginally robust enough for handling in tubular magazines. As a result, the industry has gravitated to processing such relatively delicate semiconductor packages in batches carried in recesses of rectangular trays, one example of which are so-called JEDEC trays 100 (FIG. 1). Other, even smaller semiconductor packages under current development and most recently introduced to the market include so-called “chip scale” semiconductor packages. These packages, having dimensions approximating those of a bare semiconductor die itself and employing extremely minute external connection elements, also are desirably handled in trays.
As stated, groups or lots of semiconductor devices or bare semiconductor dice consist of a particular device type and are selected to meet customer or industry standard specification. After sorting, semiconductor dice are typically marked as a group such that all semiconductor dice receive the same mark. Semiconductor dice generally undergo an array of testing during the manufacturing process and groups of semiconductor dice can be tracked through the fabrication, probe, assembly and test steps. However, this so-called lot-based manufacturing has several limitations including that it is inefficient, expensive, unreliable and impossible to achieve truly unique marking of semiconductor devices.
As a lot of semiconductor dice bearing the same identification number passes through manufacturing, data associated with the lot is generated and stored in association with the lot number. It is critical to track all semiconductor dice individually in a particular order so that test results can be correlated with the proper die. However, manufacturers must balance the benefit of identifying problems within individual semiconductor dice with the fact that maximum efficiency is achieved when a large number of semiconductor dice are tested in succession and problems are addressed only after the testing is complete. Accordingly, semiconductor dice are tested and results are recorded sequentially. To maintain accurate results, semiconductor dice must be placed and stored in carrier tubes in the identical order. The potential for error in lot-based manufacturing is very high as one misplaced semiconductor die or carrier results in inaccurate data association.
U.S. Pat. No. 5,856,923 to Jones et al. discloses a method of continuous nonlot-based integrated circuit manufacturing. In this process, each device from a mixed lot is provided either a substantially unique fuse ID code or marked on the lead frame with a substantially unique ID code (U.S. Pat. No. 6,049,624 Wilson et al.). The devices are processed and process-related data is generated for each individual device. Data relating to the particular device, rather than the entire lot, is stored in association with the substantially unique ID code.
U.S. Pat. No. 6,049,624 to Wilson et al. further discloses marking carrier trays or storage shelves with an ID code and storing the carrier tray ID code in association with the ID code for semiconductor dice. Semiconductor dice can be retrieved by lot number from the shelves or carrier trays.
It would be an improvement in the art to develop a technique of in-tray mapping and sequential unique marking of packaged semiconductor devices or bare semiconductor dice that eliminates the need for them to be pre-sorted.